Backstory:  I'm using the PayPal SANDBOX mode with a PayPal generated button.  It seems that everything at my end is working:

• The user selects items from the PayPal button, and presses SUBMIT.
• The user is taken to the PayPal SANDBOX, where they login with the SANDBOX Personal ID, and confirm the purchase.  (Even the transaction appears completed in the SANDBOX Merchant).
• Upon completion of the transaction, PayPal SANDBOX returns to the merchant link described in the PayPal Button.
• The form there looks at the tx field passed to it via the GET request, it POSTs a request to https://www.sandbox.paypal.com/cga-bin/webscr with the PayPal Identity token, gets a reply with all the transaction details, and does the database saving / email / user presentation based on it.

...in short, I can do an end-to-end without any problem.

EXCEPT...

If the user is impatient and clicks on the "If you're not redirected to John Doe's Test Store in ten seconds, click here." link, then PayPal redirects back to the right page, put only sends the ?PayerID= field.

If the user simply lets the page time out, it correctly sends the ?PayerID= field, along with the status (st=), transaction id (tx=), currency (cc=), and amount (amt=).  And, specifically, it's the transaction id that I need so I can ...well, go look up the transaction.

The PayerID isn't enough; conceivably a payer could have multiple transactions.  Without all the information passed to me, I don't even know a transaction has happened and there's money sitting in the account.

Is this a bug with PayPal?  Is it localized to just its SANDBOX?  Or is there some part of the workflow I'm missing?  Help.